Off-Road Robots Scamper Across Sand

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A six-legged, hamster-sized robot that can easily scamper across
sand, gravel and similarly unstable surfaces could lead to better
rovers for exploring Mars and other alien worlds, researchers
say.

Such robots could also find use in search-and-rescue missions;
for researchers, the robots could shed light on how animals such
as sand lizards run and how kangaroo rats hop on grainy terrains,
investigators added.

Scientists are increasingly designing robots that can go where
humans can or should not venture. To create such machines, many
inventors are taking inspiration from nature, analyzing how
animals roam across landscapes. For instance, snake-like robots
might slither into crevices to help find disaster victims.

Surfaces such as sand, gravel, soil and mud pose especially
difficult challenges since these materials can flow around legs
in ways that are often more complex than the movements of fluids
like water. To learn how to best navigate grainy surfaces,
researchers led by physicist Chen Li at the University of
California at Berkeley experimented with a six-legged droid. It
measures just 5 inches (13 centimeters) long and weighs about a
third of a pound (150 grams), or about the length and weight of a
pet hamster. Researchers used a 3D printer to create legs in a
variety of shapes, then analyzed which ones helped the robot best
scamper across poppy seeds, glass beads and natural sand. [See
also: Robot
Legs Mimic How Babies Walk ]

Robo-legs

The results of these experiments closely matched simulations the
researchers developed to predict the robot's motions. In
addition, these findings revealed laws governing the walking
behavior, which could be generalized across many different grainy
materials. The results helped refine the robot's leg shape and
walking style, with researchers arriving at a design that
optimized each of the droid's steps.

"I was floored by how well the models developed by Li and Tingnan
Zhang were able to predict the performance of the legged robots
across a range of granular materials," researcher Daniel Goldman,
a physicist at the Georgia Institute of Technology in Atlanta and
supervisor of the project, told TechNewsDaily. (In
a video,
the robot scampers along very quickly.)

In the end, the best legs were convex, made in the shape of the
letter "C." Compared to other leg designs, this shape helped the
robot sink less and move faster when traversing beds of grains.
The researchers estimate this robot reached a maximum speed of
about 1.6 mph (2.6 km/h) and took about five steps per second.

"As long as the legs are convex, the robot generates large lift
and small body drag, and thus can run fast," Goldman said. "When
the limb shape was changed to flat or concave, the performance
dropped. This information is important for optimizing the energy
efficiency and performance of
legged robots."

Although the robot
is still not quite as effective at walking across sand and gravel
as a lizard or insect, this research might help improve the
performance of roving and walking droids such as
Mars rovers.

"We can start looking at why certain desert organisms have
specific feet shapes or other adaptations that may also help them
move," Goldman said.

Animal movement

Ultimately, this work could help create and advance a field the
researchers call "terradynamics" that predicts how animals,
robots and vehicles move on grainy and other complex surfaces,
akin to how aerodynamics helps analyze motion through the air and
hydrodynamics studies movement in water.

"Just as a good understanding of aerodynamics and hydrodynamics
has allowed us to create devices with unprecedented mobility in
air and water, this work can help us take the next step — no pun
intended — toward greater mobility on more complex ground,"
Goldman told TechNewsDaily.

Future research can explore what leg and foot shapes and stride
patterns work best on surfaces made of irregularly shaped grains,
surfaces made of grains with various shapes and sloped surfaces
such as sand dunes. Studies can also investigate the benefits of
springy versus rigid limbs.

"We can also not just look at animals living now, but also ones
from the past," Goldman said. "What kind of feet did the first
animals that walked on land have? Presumably they were walking on
soft materials, since they were near the water. Did they have
limbs that helped them walk on those?"

Li, Zhang and Goldman detailed their findings in the upcoming
March 22 issue of the journal Science.